The present invention relates to an apparatus for detecting a three-dimensional structure of an object. Apparatuses for detecting 3D structures are used, for example, in industry for quality assurance. Processed surfaces can thus be examined for their quality, for example, for adherence to dimensional accuracy and/or for adherence to a predefined roughness. Furthermore, with such apparatuses it is also possible to digitally detect and three-dimensionally map entire objects.
Such an apparatus is known from U.S. Pat. No. 6,809,845 B1. This operates according to the principle of holography. Two laser beams having different wavelengths are generated by means of two lasers. Each laser beam is split into an object beam, which impinges upon an object to be measured, and a reference beam. The object beam reflected from the object and the appurtenant reference beam of one wavelength are combined and interfere with one another, the phase relationships between the two beams being recorded. A three-dimensional model of the reflected surface of the object can be created with the aid of the difference between the phase relationships produced by the laser beam having a first wavelength and the phase relationships produced by the laser beam having a second wavelength. In addition to the lasers, an Nd:YAG laser (neodymium-doped yttrium aluminum garnet laser) and an HeNe laser (helium neon laser), the apparatus comprises a plurality of mirrors, beam splitters, filters, and apertures. The required space requirement of the apparatus is large.
U.S. Pat. No. 8,068,235 B1 also discloses an apparatus for the three-dimensional detection of surface structures. Two laser sources generate a laser beam. Parts of these laser beams are combined into a composite beam, which impinges upon the object to be measured. It is then reflected by the object and detected by a camera. The remaining parts of the emitted laser beams impinge as reference beams having different angles of incidence on the camera. Since the laser beams are partially combined via beam splitters, the apparatus has an increased space requirement.
In both patent specifications, light of two or more wavelengths impinges upon the object at identical angles. This causes so-called speckle noise because as a result of the wave nature of the light in the backscattered light of a somewhat rough surface object, zones of so-called constructive (light) and destructive (dark) interference occur. The object thereby appears “granular” for the observer, which is designated as speckle or speckle noise.